The cyclic carbonate esters of vicinal diols are well known in the art and may be prepared by reacting the corresponding chlorohydrins with either sodium bicarbonate under carbon dioxide pressure or with an alkali metal carbonate. Such esters can also be produced by the reaction between vicinal chlorohydrins and diethylamine under carbon dioxide pressure. All of these processes require the use of a stoichiometric amount of base.
Another route for the preparation of cyclic alkylene carbonate esters involves the reaction between an alkylene epoxide and carbon dioxide at high pressure in liquid phase in the presence of a catalyst. Typical catalysts include quaternary ammonium halides, quaternary ammonium hydroxides, sodium bicarbonate, ion exchange resins, bis-(aminoethoxy)tin compounds and polyhalogenated 5- or 6-membered ring hydrocarbons. Such processes as these require the use of expensive alkylene epoxide as the starting material for the cyclic carbonate ester production.
Two routes for production of cyclic carbonate esters directly from olefins have appeared in the literature. According to U.S. Pat. No. 3,025,305, an olefin, carbon dioxide and oxygen are reacted in the liquid phase in the presence of a dual catalyst system. One component of the catalyst is a salt or other compound of a heavy metal and the second catalyst component is a quaternary ammonium hydroxide or halide. According to U.S. Pat. No. 4,009,183, cyclic carbonate esters are produced by the reaction between an olefin, carbon dioxide and oxygen in the presence of iodine or a metal iodide and an oxygen carrier such as activated manganese dioxide or sodium nitrite. In each of these routes the rate of carbonate ester formation is slow. In the second route, a second step is required in order to regenerate the oxygen carrier which is used in stoichiometric excess.